A method has been developed for iron-making in which metallic iron is produced by solid reduction by heating a material mixture containing an iron-oxide-containing material (iron source) such as iron ore and a carbonaceous reducing agent such as coal in a moving hearth-type reducing furnace. The material mixture used in the method is compressed into a simple compact or is agglomerated into a compact such as a pellet or a briquette, and then the resulting compact is charged into the moving hearth-type reducing furnace. When the material mixture is agglomerated, moisture is added to the material mixture to enable ready agglomeration. However, the strength of the compact is decreased with an increase in the moisture content. Thus, the stability in heat reduction operation is deteriorated. Additionally, when the moisture content of the compact is large, the rate of increase of the compact temperature in the moving hearth-type reducing furnace is decreased; which decreases the rate of reduction of iron oxide. Therefore, the compact mixed with moisture is previously dried into an agglomerated material prior to the charging of the compact into the moving hearth-type reducing furnace.
Additionally, in order to improve the handleability, the strength of the agglomerated compact is increased by blending various binders, such as slaked lime, bentonite, and carbohydrates, with the above-mentioned mixture (See, claims in Japanese Unexamined Patent Application Publication No. 11-193423). Since the strength of the agglomerated material increases in some proportion to the amount of binder, a large amount of binder is used in order to increase the strength of the agglomerated material. However, the use of a large amount of binder causes an increase in raw-material cost. Consequently, it is required that the binder content is reduced as much as possible.
Furthermore, if the moisture content when the material mixture is formed is constant, the relative content of moisture decreases with an increase in the binder content. This causes deterioration of the formability. Therefore, the moisture content is required to be increased with the binder content. However, this elongates the drying time. Thus, the production efficiency is decreased.
The present invention has been accomplished under such circumstances and an object of the present invention is to provide a method for producing an agglomerated material that is used for producing metallic iron by heat reduction in a moving hearth-type reducing furnace, wherein the agglomerated material can have a high mechanical strength without increases in the binder content and the moisture content of the material mixture.